Heat exchange system

ABSTRACT

A heat exchange system includes a fuel cell that receives a specified gas and generates electric power, a heat exchange device that exchanges heat with a heat exchange medium, a heat exchange medium passage, and a gas detector. The heat exchange medium passage allows the heat exchange medium to circulate between the heat exchange device and the fuel cell such that the heat exchange medium can exchange heat with the heat exchange device and the fuel cell. The gas detector is disposed at at least one of the heat exchange device and the heat exchange medium passage to detect the specified gas that leaks into the heat exchange medium.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2000-060806 filed onMar. 6, 2000 including the specification, drawings and abstract, isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a heat exchange system which feeds a heatexchange medium to a fuel cell so as to exchange heat with the fuelcell, or which feeds a heat exchange medium warmed through heat exchangewith a heating element, to a gas absorbing device such as a hydrogen gasabsorbing alloy tank, so as to heat the gas absorbing device.

2. Description of Related Art

In general, a fuel cell generates power in the manner as follows:hydrogen-containing fuel gas and oxygen-containing oxidizing gas aresupplied to a fuel cell, so that electrochemical reactions take place atan anode and a cathode of the cell, according to reaction formulas asindicated below.

To be more specific, when the fuel gas and the oxidizing gas aresupplied to the anode and the cathode, respectively, the reactions asrepresented by formulas (1) and (2) take place at the anode side and thecathode side, respectively, such that the fuel cell as a whole undergoesa reaction as represented by formula (3).H₂→2H⁺+2e ⁻  (1)2H⁺+2e ⁻+(1/2)O₂→H₂O  (2)H₂+(1/2)O₂→H₂O  (3)

Since these electrochemical reactions are heat generating or exothermicreactions, the inside of the fuel cell must be cooled in order toprevent the temperatures at the anode and the cathode from risingexcessively. To this end, a heat exchange system is usually provided forfeeding the fuel cell with cooling water as a heat exchange mediumcooled by a radiator, through a cooling water passage, thereby to coolthe inside of the fuel cell. One such type of heat exchange system for afuel cell is disclosed in Japanese Patent Publication No. HEI 7-66828.

In some cases, the fuel gas to be fed to the fuel cell is supplied froma hydrogen absorbing alloy tank containing a hydrogen absorbing alloy.In general, hydrogen absorbing alloys have the property of releasinghydrogen through an endothermic reaction when heated, and of absorbinghydrogen through an exothermic reaction when cooled. Therefore, in orderto extract hydrogen from the hydrogen absorbing alloy, the hydrogenabsorbing alloy inside the hydrogen absorbing alloy tank must be heatedas needed. To this end, the heat exchange system feeds the hydrogenabsorbing alloy tank with cooling water that is a heat exchange mediumwarmed by heat exchange with a heating element such as a fuel cell,through a cooling water passage, thereby to heat the inside of thehydrogen absorbing alloy tank.

Thus, the heat exchange system feeds cooling water serving as a heatexchange medium to the fuel cell in order to cool it and to the hydrogenabsorbing alloy tank in order to heat it.

In the fuel cell, the cooling water supplied to the cell is completelyseparated from the fuel gas and the oxidizing gas by separators in eachsingle cell. When the fuel cell is used for an extended period of time,however, the sealing member that seals the periphery of each separatormay deteriorate, causing the fuel gas or oxidizing gas to leak into thecooling water.

In the hydrogen absorbing alloy tank, the supplied cooling water runsthrough a tube while circulating within the tank, and is thus completelyseparated from hydrogen gas (that is, fuel gas). In some cases, the wallsurface of the tube deteriorates after an extended period of use, andthe hydrogen gas leaks into the cooling water.

In the conventional heat exchange system, however, no countermeasure hasbeen taken against leakage of the fuel gas or oxidizing gas into thecooling water as the heat exchange medium. Thus, the heat exchangesystem may suffer from deterioration of heat exchange performance due tothe presence of gas in the cooling water.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a heat exchange system whichcan minimize the possibility of a specified gas leaking into a heatexchange medium.

To accomplish at least a part of the above object, a heat exchangesystem according to the first aspect of the invention includes a fuelcell that receives a specified gas and generates electric power, a heatexchange device that performs heat exchange with a heat exchange medium,a heat exchange medium passage, and a gas detector. The heat exchangemedium passage circulates the heat exchange medium between the heatexchange device and the fuel cell such that the heat exchange medium canexchange heat with the heat exchange device and the fuel cell. A gasdetector is provided at at least one of the heat exchange device and theheat exchange medium passage at a location to detect the specified gasthat leaks into the heat exchange medium.

According to a second aspect of the invention, there is provided a heatexchange system which includes an exothermic body capable of generatingheat, a gas absorbing device comprising a gas absorbing alloy that isable to absorb or release a specified gas, a heat exchange deviceconfigured and positioned to perform heat exchange with a heat exchangemedium, a heat exchange medium passage and a gas detector. The heatexchange medium passage circulates the heat exchange medium among theheat exchange device, the exothermic body, and the gas absorbing devicesuch that the heat exchange medium can exchange heat with the heatexchange device, the exothermic body and the gas absorbing device. Thegas detector is provided at at least one of the heat exchange device andthe heat exchange medium passage at a location to detect the specifiedgas that leaks into the heat exchange medium.

In the heat exchange system of the invention as described above, evenwhere a specified gas leaks into the heat exchange medium, the gasdetector immediately detects leakage of the gas, of which the driver canbe promptly informed. Thus, the leakage of the gas into the heatexchange medium will not be left as it is, and otherwise possibledeterioration of the heat exchange performance due to bubbling of thespecified gas can be advantageously avoided.

The heat exchange system may further include a heat exchange mediumstorage device for storing at least an excess of the heat exchangemedium when the amount of the heat exchange medium that circulatesthrough the heat exchange system becomes excessive. In this case, thegas detector is provided at at least one of the heat exchange device,the heat exchange medium passage and the heat exchange medium storagedevice. The provision of the gas detector at the heat exchange mediumstorage device also yields the same advantage as described above.

Preferably, the gas detector is located at a portion of the heatexchange device or the heat exchange medium passage, which portion ishigher in position than the other portions thereof or has a largervolume than the other portions thereof.

Since gas is normally likely to collect at a location that is higher inposition or has a larger volume or capacity, the gas detector ispreferably disposed at such a location so that leakage of the specifiedgas into the heat exchange medium can be more quickly and surelydetected.

In one preferred embodiment of the invention, the heat exchange devicecomprises a radiator with a radiator cap located at the top thereof, andthe gas detector is attached to the radiator cap.

In another preferred embodiment of the invention, the heat exchangemedium storage device comprises a reserve tank, and the gas detector isattached to an upper portion of the reserve tank.

Where the radiator is used as the heat exchange device, and the reservetank is used as the heat exchange medium storage device, the gasdetector is located at the upper portion of the radiator or the reservetank which is higher in position and has a larger volume or capacity andat which the specified gas leaking into the heat exchange medium islikely to collect. Also, the gas detector provided at such a locationcan be relatively easily detached or removed, thus facilitatingmaintenance or replacement of the gas detector.

The heat exchange system of the invention is preferably installed in avehicle. In the case where a fuel cell and a hydrogen absorbing alloytank are installed in an electric vehicle or a hybrid vehicle, forexample, the heat exchange system installed in the vehicle permits earlydetection of any leakage of a specified gas into the heat exchangemedium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a heat exchange system according to afirst embodiment of the invention;

FIGS. 2A and 2B are sectional views schematically showing a stackstructure and a single cell structure, respectively, of the fuel cell ofFIG. 1;

FIG. 3 is a schematic view showing a heat exchange system according to asecond embodiment of the invention; and

FIG. 4 is a view showing an example of another location at which ahydrogen sensor may be installed.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, presently preferred embodiments of the invention will bedescribed. FIG. 1 is a schematic view showing a heat exchange systemaccording to a first embodiment of the invention.

The heat exchange system of this embodiment can cool a fuel cell 30 andheat a hydrogen absorbing alloy tank 40. The heat exchange system isinstalled in an electric vehicle or a hybrid vehicle or the like havingthe fuel cell 30 and the hydrogen absorbing alloy tank 40.

As shown in FIG. 1, the heat exchange system mainly includes a radiator10, cooling water passages 60 to 64, water pumps 70 and 76, valves 72and 74, and a reserve tank 20, and uses cooling water as a heat exchangemedium flowing through the system. As the cooling water, normal watercan be used, but it is preferable to use water to which anticorrosiveand/or antifreeze treatment(s) have been applied.

The radiator 10 is a heat exchange device for cooling the cooling waterwarmed by the fuel cell 30, and includes an upper tank 12 and a lowertank 14 for temporarily storing the cooling water, and a core 16 forpassing the cooling water. Although not shown in FIG. 1, the core 16 iscomposed of a combination of narrow water tubes through which thecooling water runs and wavy metal plates called corrugated fins, thecombination being in the form of a network.

The cooling water warmed by the fuel cell 30 flows to the upper tank 12to be temporarily stored therein and then led to the lower tank 14through the water tubes in the core 16 to be stored in the lower tank14. While the cooling water passes through the water tube, the fins thatare in contact with the tubes take away or dissipate the heat, to thuscool the cooling water. The fins are cooled by the breeze while thevehicle is running, or by a cooling fan (not shown) provided behind theradiator 10.

In this manner, the cooling water cooled and stored in the lower tank 14flows out from the lower tank 14 to reach the fuel cell 30 through thecooling water passage 60. A water pump 70 is provided midway in thecooling water passage 60 so as to forcibly circulate the cooling waterflowing through the cooling water passage 60. The water pump 70 andanother water pump 76 which will be described later are bothelectrically driven.

The cooling water which has reached the fuel cell 30 enters a manifold(not shown) that allows cooling water to flow into the fuel cell 30, andis then divided into streams flowing into cooling water channels withinrespective single cells so as to cool the anode and cathode of eachsingle cell. During the flow through the fuel cell 30, the cooling wateritself is warmed by taking heat away from the anode and the cathode ofeach cell. The streams of cooling water that have passed through thesecooling water channels again join together to reach a manifold (notshown) which allows the cooling water to flow out from the fuel cell 30.

The cooling water that flows out from the fuel cell 30 passes throughthe cooling water passage 61 and is then divided into two flow paths,one of which is led to a valve 72 and the other of which is led to avalve 74. These valves 72 and 74 selectively switch between a flow pathleading the cooling water warmed by the fuel cell 30 to the hydrogenabsorbing alloy tank 40 so as to heat the hydrogen absorbing alloy tank40, and a flow path bypassing the hydrogen absorbing alloy tank 40.

For example, when the valve 72 is closed and the valve 74 is open, thewarmed cooling water flows through the cooling water passage 62 into thehydrogen absorbing alloy tank 40 so as to heat the hydrogen absorbingalloy tank 40. On the contrary, when the valve 72 is open and the valve74 is closed, the warmed cooling water bypasses the hydrogen absorbingalloy tank 40 without being used to heat the hydrogen absorbing alloytank 40.

The hydrogen absorbing alloy tank 40 contains a hydrogen absorbing alloy42. As is well known in the art, the hydrogen absorbing alloy 42 has theproperty of releasing hydrogen through an endothermic reaction whenheated, and absorbing hydrogen through an exothermic reaction whencooled. Therefore, when it is desired to extract or take out absorbedhydrogen from the hydrogen absorbing alloy tank 40, warmed cooling wateris supplied to the hydrogen absorbing alloy tank 40 so as to heat thehydrogen absorbing alloy 42 in the hydrogen absorbing alloy tank 40 asdescribed above. On the other hand, when it is desired to store hydrogenin the hydrogen absorbing alloy tank 40, the temperature of the hydrogenabsorbing alloy 42 in the tank 40 is lowered by stopping the supply ofthe warmed cooling water to the hydrogen absorbing alloy tank 40.

When the warmed cooling water is supplied to the hydrogen absorbingalloy tank 40, the cooling water flows through a cooling water tube 44circulating within the hydrogen absorbing alloy tank 40 so as to heatthe hydrogen absorbing alloy 42 in the hydrogen absorbing alloy tank 40.

After flowing out from the hydrogen absorbing alloy tank 40, the coolingwater that heated the hydrogen absorbing alloy 42 is returned to theupper tank 12 of the radiator 10 through cooling water passages 63 and64. Midway in the cooling water passage 63, the water pump 76 isprovided for forcibly circulating the cooling water which has passedthrough the hydrogen absorbing alloy tank 40. Thus, the water pump 76 isdriven when the valve 72 is closed and the valve 74 is open.

When the cooling water is not supplied to the hydrogen absorbing alloytank 40, on the other hand, the warmed cooling water that flows out fromthe fuel cell 30 is returned to the upper tank 12 of the radiator 10after passing through the valve 72 and the cooling water passage 64.

A radiator cap 18, which also serves as a pressure regulating valve, ismounted on the top of the upper tank 12, and a cooling water tube 65extends from the radiator cap 18 to a reserve tank 20.

As shown in FIG. 1, the reserve tank 20 is a simple sealed type reservetank, and an air intake tube 66 connects to the reserve tank 20 tomaintain atmospheric pressure inside the reserve tank 20.

When the temperature of the cooling water in the upper tank 12 rises tosuch an extent that part of the water boils and the pressure within theupper tank 12 exceeds a predetermined level, cooling water and steamemitted from the tank 12 are pushed out through the cooling water tube65 into the reserve tank 20. In the reserve tank 20, the steam liquefiesand returns to water 22 without being actively cooled because of the lowambient temperature. Later, when the pressure inside the upper tank 12becomes lower than the atmospheric pressure due to a decrease in thetemperature of the cooling water in the upper tank 12, the cooling waterflows out from the reserve tank 20 and runs back to the upper tank 12through the cooling water tube 65.

The reserve tank 20 has a cooling water supply cap 24 mounted atop it.The cooling water supply cap 24 can be opened so that the cooling water22 in the reserve tank 20 can be replenished when it falls below apredetermined amount.

The heat exchange system shown in FIG. 1 has been schematicallydescribed above. Hydrogen sensors 50 and 52 and so forth, which arecharacteristic features of the invention, will be described in detaillater.

Next, a circulation path of fuel gas to be supplied from the hydrogenabsorbing alloy tank 40 to the fuel cell 30 will be briefly described.

As shown in FIG. 1, a hydrogen gas is first supplied from outside to thehydrogen absorbing alloy tank 40 through a hydrogen gas inflow passage80. At this time, if the supply of heated cooling water to the hydrogenabsorbing alloy tank 40 is stopped, and the temperature of the hydrogenabsorbing alloy tank 40 falls as described above, the supplied hydrogengas is absorbed in the hydrogen absorbing alloy 42. Then, if the supplyof the heated cooling water to the hydrogen absorbing alloy tank 40 isstarted, and the temperature inside the tank 40 rises, the hydrogen gasabsorbed in the hydrogen absorbing alloy 42 is released therefrom. Atthis moment, a valve 82 is opened, and the released hydrogen gas issupplied to the fuel cell 30 through fuel gas passages 81 and 83 toserve as fuel gas in the cell. Midway in the fuel gas passage 83 areprovided a hydrogen gas compressor 84 for circulating the hydrogen gas,a valve 85 for stopping the supply of the hydrogen gas to the fuel cell30, and a throttle valve 86 for adjusting the amount of flow of thehydrogen gas to be supplied to the fuel cell 30. The hydrogen gassupplied to the fuel cell 30 enters a manifold for fuel gas inflow andis then divided into streams flowing into fuel gas channels withinrespective single cells so that the hydrogen gas is supplied to theanode of each single cell, as will be described later. The remaininghydrogen gas that was not supplied to the anode is re-collected into amanifold for fuel gas outflow and flows out from the fuel cell 30. Thehydrogen gas thus discharged is returned again to the fuel gas passage81 through a fuel gas passage 87 and circulated.

The schematic structure of the fuel cell 30 will be describedhereinafter with reference to FIGS. 2A and 2B. FIGS. 2A and 2B aresectional views schematically showing stack structure and single cellstructure, respectively, of the fuel cell 30 as shown in FIG. 1. FIG. 2Ashows a section of the stack structure, and FIG. 2B shows a section ofthe single cell structure which is an enlargement of a portion of FIG.2A including a single cell.

As shown in FIG. 2B, a single cell is composed of an electrolyte film35, an anode 36 and a cathode 37 which are diffusion electrodes thatsandwich the film 35 from both sides, and two separators 34 whichsandwich the electrodes from both sides. The separators 34 have mutuallyopposed surfaces in which recesses are formed, and cooperate with theanode 36 and cathode 37 sandwiched between the separators 34 to form gaschannels within the single cell. Of the gas channels thus formed, gaschannels 32 formed between the separator 34 and the anode 36 allowhydrogen gas supplied as described above as fuel gas to passtherethrough, and gas channels 33 allow oxygen containing air, servingas oxidizing gas, to pass therethrough.

In the present embodiment, as shown in FIG. 2A, two adjacent separators34, which are located at intervals of two single cells, are in directcontact with each other, and have recesses formed in their opposedsurfaces such that cooling water channels 31 are formed between theadjacent separators 34. The cooling water supplied to the fuel cell 30as described above is caused to flow through the cooling water channels31.

As shown in FIG. 2A, the cooling water flowing through the cooling waterchannels 31 is usually completely separated from the hydrogen gas andoxidizing gas respectively flowing through the gas channels 32 and 33.However, as the fuel cell 30 is used for an extended period of time,cracks may be formed in the separators 34, or a sealing member (notshown) sealing the periphery of the separators 34 may deteriorate,causing the hydrogen gas (and/or the oxidizing gas) flowing through thegas channels 32 (and 33) to leak into the cooling water flowing throughthe cooling water channels 31.

In the hydrogen absorbing alloy tank 40, the supplied cooling waternormally flows through the cooling water tube 44 circulating in the tank40 while being completely separated from the hydrogen gas, as shown inFIG. 1. In some cases, however, the wall surface of the cooling watertube 44 may deteriorate after a long period of use, and the hydrogen gaspresent in the upper portion of the hydrogen absorbing alloy tank 40 mayleak into the cooling water passing through the cooling water tube 44.

If hydrogen gas leaks into the cooling water in the above manner, thehydrogen gas turns into bubbles in the cooling water, which may possiblyresult in deterioration of the heat exchange performance of the entireheat exchange system.

In view of the above problem, the present embodiment adopts thefollowing structure for detecting leakage of hydrogen gas into thecooling water early and informing the driver of the vehicle of the gasleakage.

In the heat exchange system of the present embodiment as shown in FIG.1, the hydrogen sensor 50 is mounted in the radiator cap 18 at the topof the radiator 10, and the hydrogen sensor 52 is mounted at the topportion of the reserve tank 20. Each of the hydrogen sensors 50 and 52detects even a very small amount of hydrogen if it is contained in theair, and outputs a detection signal.

The heat exchange system of the present embodiment further includes acontrol unit 90 and a hydrogen gas leakage warning lamp 92 provided onthe dashboard of the driver's seat. The control unit 90 detects theleakage of hydrogen gas into the cooling water from a detection signalreceived from the hydrogen sensors 50 and 52, and outputs a drivingsignal. The hydrogen gas leakage warning lamp 92 lights up when thedriving signal is received from the control unit 90.

When hydrogen gas leaks into the cooling water, the hydrogen gas turnsinto bubbles, which then flow through the cooling water passage togetherwith the cooling water and collect at a portion within the heat exchangesystem which is higher in position and has a relatively large capacity.To be more specific, the hydrogen gas in the form of bubbles collects atthe top portion of the upper tank 12 of the radiator 10, or around theradiator cap 18, which is located at the highest position in the heatexchange system. If the pressure inside the upper tank 12 is high, thecooling water is pushed out as described above from the upper tank 12into the reserve tank 20 through the cooling water tube 65 so that thehydrogen gas caught within the upper tank 12 is also pushed out into thereserve tank 20 along with the cooling water. The hydrogen gas pushedout together with the cooling water turns into bubbles in the coolingwater 22 and floats up to the surface of the water, to be present at thetop of the reserve tank 20.

As described heretofore, the hydrogen sensors 50 and 52 mounted in theradiator cap 18 of the radiator 10 and in the reserve tank 20,respectively, detect hydrogen gas collected at the top of the upper tank12 or at the top of the reserve tank 20 due to the leakage of thehydrogen gas into the cooling water, and output detection signals. Upondetecting the leakage of the hydrogen gas into the cooling water fromthe detection signals, the control unit 90 outputs a driving signal tothe hydrogen gas leakage warning lamp 92. The lamp 92 then lights up toinform the driver that hydrogen gas is leaking into the cooling water.

Thus, in the heat exchange system of the present embodiment, if hydrogengas leaks into the cooling water, the hydrogen sensors 50 and 52immediately detect the leakage, and the hydrogen gas leakage warninglamp 92 informs the driver of the leakage. Once the driver notices thelighting of the lamp 92, the driver can ask for an inspection of thevehicle soon in order to get repairs or replacements and so forth asnecessary. The hydrogen gas collected in the upper tank 12 of theradiator 10 and the hydrogen gas collected at the top of the reservetank 20 can be easily discharged into the air by opening the radiatorcap 18 and the cooling water supply cap 24, respectively. Moreover, thehydrogen sensors 50 and 52 are installed at sites which allow thesensors to be comparatively easily detached, which facilitates themaintenance or replacement of these hydrogen sensors.

FIG. 3 is a block diagram showing the structure of a heat exchangesystem according to a second embodiment of the invention. The heatexchange system of the present embodiment differs from the system of thefirst embodiment shown in FIG. 1 in that a completely sealed typereserve tank 100 is used instead of the simple sealed type reserve tank20. Since the other components are identical to those shown in FIG. 1,the description of these components will be omitted.

When the pressure in the upper tank 12 exceeds a predetermined level dueto a rise in the temperature of the cooling water in the upper tank 12of the radiator 10, the cooling water and steam emitted from the tank 12flow into the reserve tank 100 through a cooling water tube 68 in thesame manner as with the reserve tank 20 shown in FIG. 1. However, sincethe reserve tank 100 is of the completely sealed type unlike the reservetank 20, the cooling water never returns to the upper tank 12 from thereserve tank 100 through the cooling water tube 68 even if the pressurein the upper tank 12 falls due to a decrease in the temperature of thecooling water in the upper tank 12. Instead, the cooling water 22 in thereserve tank 100 is led to the cooling water passage 60, not through thecooling water tube 68, but through a cooling water passage 67 afterleaving an outlet formed at the bottom of the reserve tank 100.

Since hydrogen gas that leaks into the cooling water may collect at thetop of the reserve tank 100 in the present embodiment, a hydrogen sensor52 is provided at the top of the reserve tank 100 for detecting theleakage of the hydrogen gas. Thus, the present embodiment provides thesame advantages as the first embodiment. In addition, the use of thereserve tank of the completely sealed type in the present embodimenteliminates a possibility that impurities contained in the air may beintroduced into the cooling water.

While the hydrogen sensors are mounted in the radiator cap 18 of theradiator 10 and at the top of the reserve tank 20, 100 in theillustrated embodiments, such a hydrogen sensor may be installed midwayin a cooling water passage connecting the radiator 10 and the fuel cell30 or the hydrogen absorbing alloy tank 40 as shown in FIG. 4.

FIG. 4 shows an example of a location at which a hydrogen sensor may beinstalled. In FIG. 4, a portion of the cooling water passage 64 throughwhich the cooling water flows into the upper tank 12 of the radiator 10forms a circuit that projects upwards so as to bypass an obstacle(s) orthe like. Since the circuit portion of the passage 64 is higher inposition than the other portions, it is considered that hydrogen gasthat leaks into the cooling water and turns into bubbles is likely tocollect at the circuit portion. In this modified example, therefore,another hydrogen sensor 54 is provided at the circuit portion of thecooling water passage 64.

Thus, the same advantages as provided in the illustrated embodiments maybe obtained by providing an additional hydrogen sensor at a portion ofthe cooling water passage which is higher in position than the otherportions.

It is to be understood that the invention is not limited to details ofthe illustrated embodiments, but may be embodied with various changes orimprovements without departing from the scope of the invention.

In the heat exchange system of each of the above embodiments, the fuelcell 30 is cooled by using the cooling water, and the hydrogen absorbingalloy tank 40 is heated by using the cooling water that has been warmedthrough the cooling of the fuel cell 30. However, the invention is notrestricted to this type of system. For instance, the invention isapplicable to a system in which cooling water is used only to cool thefuel cell 30. In another example of the heat exchange system, thehydrogen absorbing alloy tank 40 can be heated by cooling water that hasbeen warmed not by taking heat away from the fuel cell 30 but by coolinganother heat-generating or exothermic body (auxiliary equipment or anengine in the case of a hybrid car, for example).

In the illustrated embodiments, the hydrogen sensors 50, 52, and 54detect the presence of hydrogen in the air. However, if a sensor capableof detecting the presence of hydrogen in a liquid is developed, such asensor could also be used. In that case, sensors could be installed atany location in the path through which the cooling water flows, withouttaking account of the height in position or the likelihood of collectionof hydrogen gas in the form of bubbles.

While leakage of hydrogen gas into cooling water is detected by thehydrogen sensors in the illustrated embodiments, leakage of, forexample, oxidizing gas into cooling water may be detected by using a gassensor for detecting oxidizing gas.

In the illustrated embodiments, cooling water is used as a heat exchangemedium. However, the invention is not restricted to this, but may use aheat exchange medium other than water.

In the above embodiments, the warning lamp 92 is used to visually informthe driver that hydrogen gas is leaking into the cooling water.Alternatively, a beeper or a speaker can be used to give notification bysound.

1-13. (Cancelled)
 14. A heat exchange system, comprising: an exothermicbody capable of generating heat, said exothermic body being suppliedwith a heat exchange medium for heat exchange therewith: a gas absorbingdevice comprising a gas absorbing alloy that is able to absorb orrelease a specified gas; a heat exchange device configured andpositioned to perform heat exchange with the heat exchange medium; aheat exchange medium passage that circulates the heat exchange mediumamong the heat exchange device, the exothermic body, and the gasabsorbing device such that the heat exchange medium can exchange heatwith the heat exchange device, the exothermic body and the gas absorbingdevice; and a gas detector configured and positioned at at least one ofthe heat exchange device and the heat exchange medium passage at alocation to detect the specified gas that leaks into the heat exchangemedium.
 15. A heat exchange system according to claim 14, wherein thegas detector is located at a portion of the heat exchange device or theheat exchange medium passage, which portion is higher in position thanthe other portions thereof.
 16. A heat exchange system according toclaim 14, wherein the gas detector is located at a portion of the heatexchange device or the heat exchange medium passage, which portion has alarger volume than the other portions thereof.
 17. A heat exchangesystem according to claim 14, further comprising a warning generatorthat generates a warning when the gas detector detects leakage of thespecified gas into the heat exchange medium.
 18. A heat exchange systemaccording to claim 14, wherein the specified gas comprises hydrogen, andwherein the gas detector comprises a hydrogen detector.
 19. A heatexchange system according to claim 14, wherein: the heat exchange devicecomprises a radiator with a radiator cap located at the top thereof; andthe gas detector is attached to the radiator cap.
 20. A heat exchangesystem according to claim 14, wherein the exothermic body comprises afuel cell that receives the specified gas and generates electric power.21. A heat exchange system, comprising: an exothermic body capable ofgenerating heat, said exothermic body being supplied with a heatexchange medium for heat exchange therewith; a gas absorbing devicecomprising a gas absorbing alloy that is able to absorb or release aspecified gas; a heat exchange device configured and positioned toperform heat exchange with the heat exchange medium; a heat exchangemedium passage that circulates the heat exchange medium among the heatexchange device, the exothermic body, and the gas absorbing device suchthat the heat exchange medium can exchange heat with the heat exchangedevice, the exothermic body and the gas absorbing device; a heatexchange medium storage device configured and positioned to store atleast an excess of the heat exchange medium when the amount of the heatexchange medium that circulates through the heat exchange system becomesexcessive; and a gas detector configured and positioned at at least oneof the heat exchange device, the heat exchange medium passage and theheat exchange medium storage device at a location to detect thespecified gas that leaks into the heat exchange medium.
 22. A heatexchange system according to claim 21, wherein: the heat exchange mediumstorage device comprises a reserve tank; and the gas detector isattached to an upper portion of the reserve tank.
 23. A heat exchangesystem according to claim 21, wherein the gas detector is located at aportion of the heat exchange device or the heat exchange medium passageor the heat exchange medium storage device, which portion is higher inposition than the other portions.
 24. A heat exchange system accordingto claim 21, wherein the gas detector is located at a portion of theheat exchange device or the heat exchange medium passage or the heatexchange medium storage device, which portion has a larger volume thanthe other portions thereof.
 25. A heat exchange system according toclaim 21, further comprising a warning generator that generates awarning when the gas detector detects leakage of the specified gas intothe heat exchange medium.
 26. A heat exchange system according to claim21, wherein the specified gas comprises hydrogen, and wherein the gasdetector comprises a hydrogen detector.
 27. A heat exchange systemaccording to claim 21, wherein: the heat exchange device comprises aradiator with a radiator cap located at the top thereof; and the gasdetector is attached to the radiator cap.
 28. A heat exchange systemaccording to claim 21, wherein the exothermic body comprises a fuel cellthat receives the specified gas and generates electric power. 29(Cancelled)